Continuation is proposed for a program of research upon behavioral ad biobehavioral investigations of mental retardation and intellectual development. The primary focus of the project is upon learning and its facilitation. The program of research is organized into three laboratories or research groups: Symbolic Processes, Comparative-Development, and Intrinsic Motivation. Major areas of concentration include studies of the development of perception, learning and memory processes, cognition, language, social interactions, early experience, and stress. The ultimate objective is to identify and develop strategies and procedures for enhancing the adaptation of retarded persons to normal living circumstances. A related goal is to contribute to theories and the body of data concerning cognition, learning, memory, and human development with particular reference to the role of individual differences. A wide range of research strategies are employed including basic laboratory experiments, observational studies in natural contexts, intervention procedures, longitudinal investigations, and single-subject experiments. Subjects for investigation are at-risk and normal babies, retarded people at all functional levels, peers and parents of retarded children, and infra-human species including rodents and primates.